Switching devices are utilized in a variety of industrial, commercial and consumer applications, including for example, automotive and aerospace application, along with including navigation, position sensing, current sensing, vehicle detection, and rotational displacement. Many switches rely upon magnetic sensing elements, such as Hall-effect, GMR (Giant Magnetoresistive) and AMR (Anisotropic Magnetoresistive) elements.
There are many types of magnetic sensing devices, but essentially they all provide at least one output signal that represents the magnetic field sensed by the device. The Earth, magnets, and electrical currents can all generate magnetic fields. The sensor may be able to detect the presence, the strength, and/or the direction of the magnetic field. The strength of the magnetic field may be represented by a magnitude and a polarity (positive or negative). The direction of the magnetic field may be described by its angular position with respect to the sensor. One of the benefits of using magnetic sensors is that the output of the sensor is generated without the use of contacts. This is a benefit because over time contacts can degrade and cause system failures.
A Hall-effect sensor (also referred to simply as a “Hall” sensor”) is a type of magnetic sensor that uses the Hall effect to detect a magnetic field. The Hall effect occurs when a current-carrying conductor is placed into a magnetic field. A voltage is generated perpendicular to both the current and the field. The voltage is proportional to the strength of the magnetic field to which it is exposed. The current-carrying conductor is called a Hall or Hall-effect element and it is typically composed of a semiconductor material.
Another type of magnetic sensing device is a magnetoresistive (MR) sensor, which utilizes an MR element. MR sensors are a type of magnetic sensor that uses the magnetoresistive effect to detect a magnetic field. Ferromagnetic metals, such as the nickel-iron alloy commonly known as Permalloy, alter their resistivity in the presence of a magnetic field. When a current is passed through a thin ferromagnetic film in the presence of a magnetic field, the voltage will change. This change in voltage represents the strength or direction of the magnetic field. By designing an MR sensor in a Wheatstone bridge configuration, either the strength or direction of the magnetic field can be measured. MR sensors provide a high-sensitivity and high-accurate output. A device related to an MR element is a GMR (Giant Magnetoresistive) element.
One of the problems with conventional switching devices employing such magnetic sensing elements is that these types of devices are very sensitive to magnet and magnetic sensing element tolerances, which results in a low accuracy at the switching point and/or increased assembly mechanical tolerances required to achieve prescribed accuracies. A typical conventional switching device of this type employs only two magnets in a dual magnet configuration with respect to a Hall-effect or magnetic sensing element. A new configuration is therefore required, which overcomes these drawbacks, and which is generally more efficient and accurate than such conventional devices.